A TD-SCDMA system typically has a high demand for synchronization that has a great impact upon channel estimation. If there is no exact system synchronization, channel estimation can be out of window, and interferences among the system users can be great. Such interferences cannot be easily addressed. Therefore, in the access process of User Apparatus (UE) in the TD-SCDMA system, synchronization of the network side and UE should first be established. At the side of the base station, there is simultaneous access of multi-users and multi-uplink codes. Also, because of channel fading and multi-path delay, the peak value of the base station after correlation cannot reach a preset threshold, or there can be multi-peak values. Therefore, two negative aspects can arise: on one hand, the base station might have inaccurate estimation of the original synchronization of the UE, which is not favorable for synchronization setup and track. On the other hand, because of the correlation result for the multi-path condition (especially case 2, shown in Table 1) and the collision of two UE uplink synchronization codes is quite close, the collision and multi-path conditions cannot be differentiated at the base station side and can cause the original synchronization to fail.
In the TD-SCDMA system, the uplink and downlink employ the same frequency. For a time period, the downlink and uplink have the approximately similar radio propagation environment. Therefore, the channel impact of the uplink and the downlink correlate with each other in the time period, and can be identified as approximately equal.
TABLE 1the multi-path propagation model of TD-SCDMA systemCase 1, speed 3 km/hCase 2, speed 3 km/hCase 3, speed 120 km/hRelativeRelativeRelativeRelativeRelativeRelativeDelayMean PowerDelayMean PowerDelayMean Power[ns][dB][ns][dB][ns][dB]0000002928−1029280781−31200001563−62344−9
In May 2000, P. W. Baier from Kaiserslautern, Germany, and his colleagues proposed pre-equalization of multi-user environment in the Time Division Duplex Code Division Multiple Access (TDD-CDMA) mode, which is a related technology of joint detection at the side of uplink base station. This technology combines uplink JD, channel status information and pre-adaptation equalization, and constructs the multi-path and multi-address transmission signal basing on all the users. In this way, the mobile station does not need to undertake the complex channel estimation, but only simple calculation to detect the signals. JD technology has already been tested in both theories and practice. Chinese Patent Application No. of 03137628.2, titled “Joint Optimization Signal Methods of Joint Transmission Technology,” which is based on Joint Detection, further proposed that JT Transmission technology, which corresponds to JD technology. According to this technology, the JD requirement of UE is shifted to the JT to the base station, and UE needs simple operation to detect the signals, so as to meet the target of decreasing the UE complexity. In this way, on one hand, JT can effectively decrease the multi-address and multi-path interferences to improve the system capacity; on the other hand, after the downlink implements JT technology, there is no need for a mobile station to undertake channel estimation, but only simple calculation to detect the signals to decrease the processing complexity and power consumption of the mobile station. However, JT technology based on UE has never been disclosed until now.
The frame structure of TD-SCDMA system is shown in FIG. 1. Three time slots DwPTS, GP, and UpPTS can be further separated into the following time slots: Gp1=16 chips, GP2=32 chips, SYNC_DL1=64 chips, Gp3=96 chips, SYNC_UL=128 chips, GP4=32 chips. According to the structure in FIG. 1, suppose UE undertakes JT based on the TS0 downlink channel estimation, and transmits UpPTS when UpPTS is started, the middle interval is Gp1+Gp2+SYNC_DL1+Gp3=208 chips, approximately τ=5/6400*192=0.1625 ms. According to the coefficient ratio formula,
            R      R        ⁡          (      τ      )        =            1      N        ⁢    cos    ⁢                  ⁢          ϖ      c        ⁢    τ    ⁢                  ∑                  n          =          1                N            ⁢              cos        ⁡                  (                                    ϖ              m                        ⁢            τ            ⁢                                                  ⁢            cos            ⁢                                          2                ⁢                π                ⁢                                                                  ⁢                n                            N                                )                    where ωc is carrier wave, and ωm is the maximum Dopler shift, N is the number of the low frequency oscillators, τ is the time interval, whose coefficient ratio is 0.9997.
FIG. 2 shows the coefficient ratio of the mobile speed at 120 km/h, and time is 10s. It shows that the uplink synchronization theory based on the JT technology is feasible. Hence this invention proposes a method and system for the uplink synchronization based on JT technology.